Unions hailed a strike by up to two million public sector workers as "historic" tonight as they angrily rejected claims by the Prime Minister that the biggest walkout in a generation had been a "damp squib".

David Cameron told the Commons that the "irresponsible and damaging" industrial action had been far from universally supported as he defended the Government's controversial pension reforms.

Officials from 30 unions involved in today's strike reported huge support, with up to 90% of some organisations taking action, often for the first time in their lives.

The strike closed more than three quarters of schools in England, as well as courts, museums, libraries and jobcentres, disrupted transport, hospitals and Government departments, led to around 15% of driving tests being cancelled, and was described by unions as the biggest since the 1979 Winter of Discontent.

Physiotherapists, headteachers, librarians, lollipop ladies, refuse collectors, weather forecasters and scientists were among those involved in the stoppage.

Civil service union Prospect said action by 26,000 of its members alone disrupted or stopped work at more than 400 locations, ranging from Ministry of Defence sites to prisons.

More than 1,000 rallies were held across the UK, including one in central London attended by tens of thousands of workers, some accompanied by their children.

Len McCluskey, leader of Unite, said the rally showed the depth of anger among public sector workers, adding: "The Prime Minister is completely out of touch. I have been to 12 picket lines and there has been a fantastic response both from workers and the general public.

"The Government can try to spin and tell lies, but they have been found out."

University and College Union leader Sally Hunt said: "Cheap potshots add nothing to what should be a serious debate about millions of people's futures, and just expose how out of touch the Prime Minister really is."

Warnings of massive delays at Heathrow airport failed to materialise, with passengers saying border controls were "better than usual".

Union officials accused the Government of "ramping up" possible airport disruption and claimed that "under-trained" staff had been drafted in to cover striking immigration and passport workers.

Debbie Arnell, a 42-year-old apprenticeship assessor from Bournemouth who had flown back to Heathrow's terminal five after a holiday in Philadelphia, said there appeared to be "more staff than usual" at passport control.

Colin Matthews, chief executive of airport operator BAA, said: "Due to the effective contingency plans we put in place with airlines and the UK Border Agency, immigration queues are currently running at normal levels for Heathrow.

"As a result of the whole airport community working together over the past few days we have more immigration officers on duty and fewer passengers arriving than would otherwise be the case. That has put us in a better place to avoid the serious delays and widespread disruption at Heathrow that were projected last week."

The Public and Commercial Services union reported a "huge" turnout for the strike, with up to 90% of staff in some Government departments, including Revenue and Customs, taking action.

Unison leader Dave Prentis said: "I wouldn't call two million people taking strike action a damp squib. Cameron is sounding increasingly desperate in his attacks on public service workers.

"He has only to turn on the TV, or listen to the radio - or look out the window - to see the nurses, dinner ladies, paramedics, social workers, teaching assistants, lollipop ladies amongst others standing up for their pensions. And the thousands of picket lines, demonstrations, rallies and events are not a figment of our imagination. These people are angry public servants who the Government has driven to the end of their tether."

A "handful" of staff from 10 Downing Street went on strike, and the school attended by Mr Cameron's son Elwen, was closed.

The Department of Health told NHS trusts in England they must not release figures regarding staff on strike or the number of cancelled operations and appointments, it was revealed.

A letter said a "national position" statement must be sent to the media ahead of any regional breakdowns.

Christina McAnea, head of health at Unison, said: "It is outrageous that the Department of Health are desperately trying to hide the fact that NHS services are being disrupted across the UK. Our members are reporting fantastic support for the day of action.

"We appreciate that this will cause difficulty for patients but we have made sure that patient safety will not be compromised."

Mr McCluskey said it was a "diabolical" attempt to "distort the truth".

The London Ambulance Service revealed that 42% of its staff were on strike, saying it was under "increased pressure" after receiving 30% more 999 calls than normal.

In Salford, Greater Manchester, council binmen manned a picket line outside their depot. Standing around a burning brazier to keep warm, they held placards including one asking: "Do we look Gold Plated?"

Primary schoolteacher Teresa Hughes, 48, of Newport, South Wales, who joined a rally in Swansea, said: "I am the main earner in my family and teachers like me are having to work more but for less.

"I don't think anyone wanted to go on strike, and we don't take a decision like this lightly. But ask anyone here today and they will tell you they feel like they have been left little choice but to take part in industrial action. The fact that the Government has reneged on its pension deal does not give us much faith."

Cabinet Office minister Francis Maude said the strike was "inappropriate, untimely and irresponsible", adding: "Responsibility for any disruption which people may experience today lies squarely with union leaders.

"Claims that there are no negotiations going on are simply not true. There were formal discussions with the civil service unions only yesterday and there will be formal discussions with the teaching unions tomorrow and health on Friday.

"In addition, there are frequent informal contacts between the Government and the TUC. All of this underlines how indefensible today's strike is while these talks at scheme level are moving forward."

The Chartered Society of Physiotherapy (CSP) said 90% of its 23,000 NHS members were estimated to be on strike, for only the second time in the union's 117-year history.

Alex MacKenzie, of the CSP, said: "Physiotherapy staff have demonstrated their anger over these pensions proposals by turning out in huge numbers today. No-one wanted to strike, but our members felt we had to take a stand."